1. Field of the Invention
The present invention relates to an improvement in an exhaust muffler with an exhaust emission control function, which is utilized mainly in a general-purpose engine.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 5-141233 discloses a conventional exhaust muffler with an exhaust emission control function, in which a porous carrier carrying an exhaust emission control catalyst is secured to an inner surface of a hollow muffler body. Also, Japanese Patent No. 2618764 discloses another conventional exhaust muffler with an exhaust emission control function, in which a honeycomb carrier or a porous carrier carrying an exhaust emission control catalyst is incorporated in an exhaust passage within a hollow muffler body.
In the exhaust muffler as disclosed in Japanese Patent Application Laid-open No. 5-141233, the porous carrier carrying the exhaust emission control catalyst is secured to the inner wall of the muffler body, and therefore the muffler body is overheated by exhaust gas purifying reaction heat generated in the exhaust emission control catalyst, resulting in a fear that thermal damages are provided to devices adjacent to the exhaust muffler. In addition, in the exhaust muffler as disclosed in Japanese Patent No. 2618764, not only the structure is complicated and costly, but also the temperature of the exhaust gas is steeply raised and a portion of the muffler body near or adjacent to the honeycomb carrier or the porous carrier is particularly overheated because the purification of an exhaust gas is conducted at one time on the honeycomb carrier or the porous carrier. Further, a slight loss in output is caused by an increase in back pressure in the engine due to the honeycomb carrier or the porous carrier. Therefore, this exhaust muffler is unsuitable for use, particularly, in a general-purpose engine having a relatively small displacement.